import { useCallback, useEffect, useRef, useState } from "react";
import { useTranslation } from "react-i18next";
import { keepPreviousData, useInfiniteQuery, useQuery, useQueryClient } from "@tanstack/react-query";
import { ArrowDown, ArrowUp, ArrowLeft, RefreshCw, Youtube } from "lucide-react";
import { api, HttpError, type FeedFilters, type Video } from "../lib/api";
import i18n from "../i18n";
import { notify, resolveVideo } from "../lib/notifications";
import { useDebounced } from "../lib/useDebounced";
import VirtualFeed from "./VirtualFeed";
import PlayerModal from "./PlayerModal";

const PAGE = 60;

// The "Show" view filter, content-type filter and ordering live in the feed toolbar
// (above the cards), not the filter sidebar.
const SHOW_IDS = ["unwatched", "in_progress", "all", "watched", "hidden"];
const CONTENT = [
  { key: "includeNormal", label: "sidebar.content.normal" },
  { key: "includeShorts", label: "sidebar.content.shorts" },
  { key: "includeLive", label: "sidebar.content.live" },
] as const;
const rollSeed = () => Math.floor(Math.random() * 1_000_000_000);

// Ordering = a key + direction (like the Playlists page), mapped to the backend sort strings
// (which encode both). One entry per concept; a single arrow flips the direction.
// "relevance" (full-text search ranking) and "shuffle" are directionless single-string sorts.
type SortKey = "date" | "popular" | "duration" | "title" | "subscribers" | "priority" | "shuffle" | "relevance";
const SORT_KEYS: SortKey[] = ["date", "popular", "duration", "title", "subscribers", "priority", "shuffle"];
const DIRECTIONLESS: SortKey[] = ["shuffle", "relevance"];
const SORT_MAP: Record<Exclude<SortKey, "shuffle" | "relevance">, { asc: string; desc: string }> = {
  date: { desc: "newest", asc: "oldest" },
  popular: { desc: "views", asc: "views_asc" },
  duration: { desc: "duration_desc", asc: "duration_asc" },
  title: { asc: "title", desc: "title_desc" },
  subscribers: { desc: "subscribers", asc: "subscribers_asc" },
  priority: { desc: "priority", asc: "priority_asc" },
};
const SORT_DEFAULT_DIR: Record<Exclude<SortKey, "shuffle" | "relevance">, "asc" | "desc"> = {
  date: "desc", popular: "desc", duration: "desc", title: "asc", subscribers: "desc", priority: "desc",
};
function parseSort(s: string): { key: SortKey; dir: "asc" | "desc" } {
  if (s === "shuffle" || s === "relevance") return { key: s, dir: "desc" };
  for (const k of Object.keys(SORT_MAP) as (keyof typeof SORT_MAP)[]) {
    if (SORT_MAP[k].asc === s) return { key: k, dir: "asc" };
    if (SORT_MAP[k].desc === s) return { key: k, dir: "desc" };
  }
  return { key: "date", dir: "desc" };
}
function buildSort(key: SortKey, dir: "asc" | "desc"): string {
  if (key === "shuffle" || key === "relevance") return key;
  return SORT_MAP[key][dir];
}

function matchesView(status: string, show: string): boolean {
  switch (show) {
    case "hidden":
      return status === "hidden";
    case "watched":
      return status === "watched";
    case "unwatched":
    case "in_progress":
      // (in_progress is further narrowed server-side by resume position; here we only
      // need to drop a card once it's optimistically marked watched/hidden.)
      return status !== "watched" && status !== "hidden";
    default:
      return status !== "hidden"; // all
  }
}

export default function Feed({
  filters,
  setFilters,
  view,
  canRead,
  isDemo = false,
  onOpenWizard,
  ytSearch,
  onYtSearch,
  onExitYtSearch,
  onOpenChannel,
  channelScoped,
}: {
  filters: FeedFilters;
  setFilters: (f: FeedFilters) => void;
  view: "grid" | "list";
  canRead: boolean;
  isDemo?: boolean;
  onOpenWizard: () => void;
  // Live YouTube search: the active search term (null = normal feed). Entering a search and
  // leaving it both step browser history (the search is a feed sub-view with its own history
  // entry), so the empty-state CTA enters via onYtSearch and "back to feed" pops via
  // onExitYtSearch. Search affordances are hidden for demo.
  ytSearch: string | null;
  onYtSearch: (q: string) => void;
  onExitYtSearch: () => void;
  // Open a channel's dedicated page (from a card's channel name / avatar). Threaded down to
  // the cards via VirtualFeed.
  onOpenChannel?: (channelId: string, channelName?: string) => void;
  // True when this feed is scoped to a single channel (the channel page). Drops sort options
  // that are constant within one channel (subscribers, priority) — they'd be meaningless.
  channelScoped?: boolean;
}) {
  const { t } = useTranslation();
  const sortKeys = channelScoped
    ? SORT_KEYS.filter((k) => k !== "subscribers" && k !== "priority")
    : SORT_KEYS;
  const [overrides, setOverrides] = useState<Record<string, string>>({});
  const [savedOverrides, setSavedOverrides] = useState<Record<string, boolean>>({});
  // The open player: which video and where to start (null = resume from saved position).
  const [activeVideo, setActiveVideo] = useState<{ video: Video; startAt: number | null } | null>(
    null
  );
  const qc = useQueryClient();

  const openVideo = useCallback(
    (video: Video, startAt: number | null = null) => setActiveVideo({ video, startAt }),
    []
  );

  const ytActive = !!ytSearch;

  // Debounce only the search term feeding the queries: the input still updates instantly (it
  // owns filters.q), but the feed/count keys settle after a pause, so typing doesn't refetch —
  // and re-fetched pages keep the previous results on screen, so the feed never blanks/flickers.
  const debouncedQ = useDebounced(filters.q, 300);
  const queryFilters: FeedFilters = { ...filters, q: debouncedQ };

  const query = useInfiniteQuery({
    queryKey: ["feed", queryFilters],
    queryFn: ({ pageParam }) => api.feed(queryFilters, pageParam as string | null, PAGE),
    initialPageParam: null as string | null,
    getNextPageParam: (last) => last.next_cursor ?? undefined,
    enabled: !ytActive, // don't load the normal feed while showing live YouTube results
    placeholderData: keepPreviousData,
  });

  // Live YouTube search results. We never auto-paginate on scroll — the user pulls more with an
  // explicit button (each api-source page spends 100 quota units; scrape-source pages are free).
  // retry:false so a 429 (quota/limit) surfaces at once for inline display. staleTime keeps a
  // revisited search from re-spending.
  const ytQuery = useInfiniteQuery({
    queryKey: ["yt-search", ytSearch],
    queryFn: ({ pageParam }) => api.searchYoutube(ytSearch as string, pageParam as string | null),
    initialPageParam: null as string | null,
    getNextPageParam: (last) => last.next_cursor ?? undefined,
    enabled: ytActive,
    staleTime: 5 * 60_000,
    retry: false,
  });

  // Switching to the relevance sort when a search starts happens atomically in the header's
  // input onChange (race-free with the query update). Here we only handle the reverse: when
  // the term is cleared, fall back to the default sort — relevance has no dropdown option and
  // doesn't rank without a query.
  const qEmpty = !filters.q.trim();
  useEffect(() => {
    if (qEmpty && parseSort(filters.sort).key === "relevance") {
      setFilters({ ...filters, sort: buildSort("date", "desc") });
    }
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [qEmpty]);

  // Drop optimistic status overrides when filters change OR fresh server data
  // arrives — after a refetch the server is authoritative, so a stale override
  // (e.g. a video reverted to "new" from the notification center) won't keep it
  // filtered out of the current view.
  useEffect(() => {
    setOverrides({});
    setSavedOverrides({});
  }, [filters]);
  useEffect(() => {
    setOverrides({});
    setSavedOverrides({});
  }, [query.dataUpdatedAt]);

  const countQuery = useQuery({
    queryKey: ["feed-count", queryFilters],
    queryFn: () => api.feedCount(queryFilters),
    staleTime: 30_000,
    enabled: !ytActive,
    placeholderData: keepPreviousData,
  });

  const { hasNextPage, isFetchingNextPage, fetchNextPage } = query;

  // Keep the loaded videos in a ref so onState can stay referentially stable
  // (it needs the list only to look up a title for the notification). A stable
  // onState lets memo(VideoCard) skip re-rendering existing cards on page append.
  const loadedRef = useRef<Video[]>([]);

  const onState = useCallback(
    (id: string, status: string) => {
      setOverrides((o) => ({ ...o, [id]: status }));
      // Refetch once the server has the change so other views (e.g. Hidden) are in sync.
      // Announce the change only AFTER the server confirms it: a "Marked watched"/"Hidden"
      // notice (or resolving a stale one) is a claim of success, so firing it optimistically
      // would falsely report a change that the .catch below is about to roll back (e.g. when
      // the API is unreachable).
      api
        .setState(id, status)
        .then(() => {
          qc.invalidateQueries({ queryKey: ["feed"] });
          if (status === "hidden") {
            const v = loadedRef.current.find((x) => x.id === id);
            notify({
              message: v?.title
                ? i18n.t("feed.hiddenNamed", { title: v.title })
                : i18n.t("feed.hidden"),
              action: { label: i18n.t("feed.undo"), onClick: () => onState(id, "new") },
              meta: {
                kind: "video-hidden",
                videoId: id,
                title: v?.title ?? "this video",
                channelId: v?.channel_id ?? "",
                channelName: v?.channel_title ?? "",
              },
            });
          } else if (status === "watched") {
            const v = loadedRef.current.find((x) => x.id === id);
            notify({
              message: v?.title
                ? i18n.t("feed.markedWatchedNamed", { title: v.title })
                : i18n.t("feed.markedWatched"),
              action: { label: i18n.t("feed.unwatch"), onClick: () => onState(id, "new") },
              meta: {
                kind: "video-watched",
                videoId: id,
                title: v?.title ?? "this video",
                channelId: v?.channel_id ?? "",
                channelName: v?.channel_title ?? "",
              },
            });
          } else if (status === "new") {
            // Unhide / unwatch (from a card, the toast's Undo, or the center): quietly resolve
            // any stale hide/watch notice for this video so it doesn't linger with a dead action.
            resolveVideo(id);
          }
        })
        .catch(() =>
          // Server rejected the change — drop the optimistic override so the card
          // reverts to the real (unchanged) state instead of staying phantom-hidden.
          setOverrides((o) => {
            const next = { ...o };
            delete next[id];
            return next;
          })
        );
    },
    [qc]
  );

  const onResetState = useCallback(
    (id: string) => {
      // Reset to pristine (drop the whole VideoState row, incl. resume position) — the
      // un-watch toggle can't clear an in-progress position, this can.
      setOverrides((o) => ({ ...o, [id]: "new" }));
      api
        .clearState(id)
        .then(() => qc.invalidateQueries({ queryKey: ["feed"] }))
        .catch(() =>
          setOverrides((o) => {
            const next = { ...o };
            delete next[id];
            return next;
          })
        );
    },
    [qc]
  );

  const handleOpenChannel = useCallback(
    (channelId: string, channelName: string) => {
      onOpenChannel?.(channelId, channelName);
    },
    [onOpenChannel]
  );

  const onToggleSave = useCallback(
    (id: string, saved: boolean) => {
      setSavedOverrides((o) => ({ ...o, [id]: saved }));
      (saved ? api.watchLaterAdd(id) : api.watchLaterRemove(id))
        .then(() => {
          qc.invalidateQueries({ queryKey: ["playlists"] });
          qc.invalidateQueries({ queryKey: ["playlist"] });
        })
        .catch(() => setSavedOverrides((o) => ({ ...o, [id]: !saved })));
    },
    [qc]
  );

  const loaded: Video[] = (query.data?.pages ?? []).flatMap((p) => p.items);
  loadedRef.current = loaded;
  const items: Video[] = loaded
    .map((v) => (overrides[v.id] ? { ...v, status: overrides[v.id] } : v))
    .map((v) => (savedOverrides[v.id] !== undefined ? { ...v, saved: savedOverrides[v.id] } : v))
    .filter((v) => matchesView(v.status, filters.show));

  // --- Live YouTube search mode -------------------------------------------------------------
  // A separate data source rendered in the same cards/player. No watch-state view filter (the
  // user explicitly searched, so show everything) and no auto-pagination (each page costs quota).
  if (ytActive) {
    const ytLoaded: Video[] = (ytQuery.data?.pages ?? []).flatMap((p) => p.items);
    loadedRef.current = ytLoaded;
    const ytItems: Video[] = ytLoaded
      .map((v) => (overrides[v.id] ? { ...v, status: overrides[v.id] } : v))
      .map((v) => (savedOverrides[v.id] !== undefined ? { ...v, saved: savedOverrides[v.id] } : v));
    const ytError =
      ytQuery.error instanceof HttpError
        ? ytQuery.error.detail || t("feed.yt.error")
        : ytQuery.isError
          ? t("feed.yt.error")
          : null;
    // The backend reports which source served the search; scrape spends no search quota, so we
    // drop the quota warning + "uses quota" wording in that mode.
    const zeroQuota = ytQuery.data?.pages?.[0]?.source === "scrape";

    return (
      <div className="p-4">
        <div className="flex items-center gap-2 flex-wrap pb-3 mb-1 border-b border-border">
          <button
            onClick={() => {
              // The search just ingested new catalog videos, so the normal feed (which was
              // disabled and still holds its pre-search cache) is stale. Drop those caches so
              // it re-fetches fresh on return instead of showing the old (often empty) result.
              // Surface the just-searched videos in the feed you return to: switch the Source
              // filter to "search" (your own search finds) and rank them by relevance.
              setFilters({ ...filters, librarySource: "search", sort: "relevance" });
              onExitYtSearch();
              qc.removeQueries({ queryKey: ["feed"] });
              qc.removeQueries({ queryKey: ["feed-count"] });
              qc.removeQueries({ queryKey: ["facets"] });
            }}
            className="inline-flex items-center gap-1.5 text-sm text-muted hover:text-accent transition shrink-0"
          >
            <ArrowLeft className="w-4 h-4" />
            {t("feed.yt.back")}
          </button>
          <span className="mx-1 h-5 w-px bg-border" aria-hidden="true" />
          <Youtube className="w-4 h-4 text-accent shrink-0" />
          <span className="text-sm font-semibold truncate">
            {t("feed.yt.resultsFor", { query: ytSearch })}
          </span>
          <span className="text-xs text-muted">
            {zeroQuota ? t("feed.yt.freeNote") : t("feed.yt.quotaNote")}
          </span>
        </div>

        {ytQuery.isLoading ? (
          <div className="py-16 text-center text-muted">{t("feed.yt.searching")}</div>
        ) : ytError ? (
          <div className="py-16 text-center text-muted max-w-md mx-auto">{ytError}</div>
        ) : ytItems.length === 0 ? (
          <div className="py-16 text-center text-muted">{t("feed.yt.noResults")}</div>
        ) : (
          <>
            <VirtualFeed
              items={ytItems}
              view={view}
              onState={onState}
              onToggleSave={onToggleSave}
              onOpenChannel={handleOpenChannel}
              onResetState={onResetState}
              onOpen={openVideo}
              hasNextPage={false}
              isFetchingNextPage={false}
              fetchNextPage={() => {}}
            />
            {ytQuery.hasNextPage && (
              <div className="text-center pt-4">
                <button
                  onClick={() => ytQuery.fetchNextPage()}
                  disabled={ytQuery.isFetchingNextPage}
                  className="inline-flex items-center gap-2 px-4 py-2 rounded-xl border border-border bg-card text-sm font-medium hover:border-accent hover:text-accent disabled:opacity-50 transition"
                >
                  {ytQuery.isFetchingNextPage
                    ? t("feed.loadingMore")
                    : zeroQuota
                      ? t("feed.yt.loadMoreFree")
                      : t("feed.yt.loadMore")}
                </button>
              </div>
            )}
          </>
        )}

        {activeVideo && (
          <PlayerModal
            video={activeVideo.video}
            startAt={activeVideo.startAt}
            onClose={() => setActiveVideo(null)}
            onState={onState}
            onOpenChannel={onOpenChannel}
          />
        )}
      </div>
    );
  }

  if (query.isLoading) return <div className="p-8 text-muted">{t("feed.loading")}</div>;
  if (query.isError) return <div className="p-8 text-muted">{t("feed.loadError")}</div>;
  // Empty "my" feed with no YouTube access. The shared demo account can never connect
  // YouTube, so it gets a gentle nudge into the shared library instead of the connect
  // wizard; real users get the onboarding prompt. No toolbar (sort/type are meaningless).
  if (items.length === 0 && !canRead && filters.scope === "my")
    return (
        <div className="p-8 grid place-items-center text-center">
          <div className="max-w-sm">
            <h2 className="text-lg font-semibold">
              {isDemo ? t("feed.demoEmptyTitle") : t("feed.emptyTitle")}
            </h2>
            <p className="text-sm text-muted mt-2 mb-4">
              {isDemo ? t("feed.demoEmptyBody") : t("feed.emptyBody")}
            </p>
            {isDemo ? (
              <button
                onClick={() => setFilters({ ...filters, scope: "all" })}
                className="inline-flex items-center justify-center gap-2 px-5 py-2.5 rounded-xl font-semibold bg-accent text-accent-fg hover:opacity-90 transition"
              >
                {t("feed.browseLibrary")}
              </button>
            ) : (
              <>
                <button
                  onClick={onOpenWizard}
                  className="inline-flex items-center justify-center gap-2 px-5 py-2.5 rounded-xl font-semibold bg-accent text-accent-fg hover:opacity-90 transition"
                >
                  {t("feed.setUp")}
                </button>
                <button
                  onClick={() => setFilters({ ...filters, scope: "all" })}
                  className="block mx-auto mt-3 text-sm text-muted hover:text-accent transition"
                >
                  {t("feed.browseShared")}
                </button>
              </>
            )}
          </div>
        </div>
      );

  const { key: sortKey, dir: sortDir } = parseSort(filters.sort);

  const toolbar = (
    <div className="pb-3">
      <div className="flex items-center gap-1.5 gap-y-2 flex-wrap">
        {SHOW_IDS.map((id) => (
          <button
            key={id}
            onClick={() => setFilters({ ...filters, show: id })}
            aria-pressed={filters.show === id}
            className={`text-xs px-3 py-1.5 rounded-full border transition ${
              filters.show === id
                ? "bg-accent text-accent-fg border-accent"
                : "border-border text-muted hover:text-fg hover:border-accent"
            }`}
          >
            {t("sidebar.show." + id)}
          </button>
        ))}
        <span className="mx-1 h-5 w-px bg-border" aria-hidden="true" />
        {CONTENT.map((c) => {
          const on = filters[c.key];
          return (
            <button
              key={c.key}
              onClick={() => setFilters({ ...filters, [c.key]: !on })}
              aria-pressed={on}
              className={`text-xs px-3 py-1.5 rounded-full border transition ${
                on
                  ? "bg-accent text-accent-fg border-accent"
                  : "border-border text-muted hover:text-fg hover:border-accent"
              }`}
            >
              {t(c.label)}
            </button>
          );
        })}
        {(
          <>
            <span className="mx-1 h-5 w-px bg-border" aria-hidden="true" />
            <label className="inline-flex items-center gap-1.5 text-xs text-muted">
              <span>{t("feed.source.label")}</span>
              <select
                value={filters.librarySource ?? "organic"}
                onChange={(e) =>
                  setFilters({
                    ...filters,
                    librarySource: e.target.value as FeedFilters["librarySource"],
                  })
                }
                title={t("feed.source.tip")}
                className="bg-card border border-border rounded-lg px-2 py-1 text-xs outline-none focus:border-accent"
              >
                <option value="organic">{t("feed.source.organic")}</option>
                <option value="all">{t("feed.source.all")}</option>
                <option value="search">{t("feed.source.only")}</option>
              </select>
            </label>
          </>
        )}
        <span className="mx-1 h-5 w-px bg-border" aria-hidden="true" />
        <span className="text-xs text-muted whitespace-nowrap">
          {countQuery.data
            ? t("feed.videoCount", {
                count: countQuery.data.count,
                formattedCount: countQuery.data.count.toLocaleString(),
              })
            : " "}
        </span>
        <div className="ml-auto flex items-center gap-2">
          <span className="text-xs text-muted">{t("feed.sortLabel")}</span>
        <select
          value={sortKey}
          onChange={(e) => {
            const key = e.target.value as SortKey;
            const dir = DIRECTIONLESS.includes(key)
              ? "desc"
              : SORT_DEFAULT_DIR[key as Exclude<SortKey, "shuffle" | "relevance">];
            setFilters({
              ...filters,
              sort: buildSort(key, dir),
              seed: key === "shuffle" ? rollSeed() : undefined,
            });
          }}
          className="bg-card border border-border rounded-lg px-2 py-1.5 text-sm outline-none focus:border-accent"
        >
          {/* Relevance only ranks meaningfully when there's a search term — offer it then. */}
          {(filters.q.trim() ? (["relevance", ...sortKeys] as SortKey[]) : sortKeys).map((k) => (
            <option key={k} value={k}>
              {t("feed.sortKey." + k)}
            </option>
          ))}
        </select>
        {!DIRECTIONLESS.includes(sortKey) && (
          <button
            onClick={() =>
              setFilters({ ...filters, sort: buildSort(sortKey, sortDir === "asc" ? "desc" : "asc") })
            }
            title={sortDir === "asc" ? t("feed.dirAsc") : t("feed.dirDesc")}
            aria-label={sortDir === "asc" ? t("feed.dirAsc") : t("feed.dirDesc")}
            className="shrink-0 p-1.5 rounded-lg border border-border bg-card text-fg hover:border-accent hover:text-accent active:translate-y-px transition"
          >
            {sortDir === "asc" ? <ArrowUp className="w-4 h-4" /> : <ArrowDown className="w-4 h-4" />}
          </button>
        )}
        {sortKey === "shuffle" && (
          <button
            onClick={() => setFilters({ ...filters, seed: rollSeed() })}
            title={t("sidebar.reshuffle")}
            aria-label={t("sidebar.reshuffle")}
            className="shrink-0 p-1.5 rounded-lg border border-border bg-card text-fg hover:border-accent hover:text-accent active:translate-y-px transition"
          >
            <RefreshCw className="w-4 h-4" />
          </button>
        )}
        </div>
      </div>
    </div>
  );

  return (
    <div className="p-4">
      {toolbar}
      {items.length === 0 ? (
        <div className="py-16 text-center text-muted">
          <p>{t("feed.noMatches")}</p>
          {filters.q.trim() && !isDemo && (
            <button
              onClick={() => onYtSearch(filters.q.trim())}
              className="mt-4 inline-flex items-center gap-2 px-4 py-2 rounded-xl font-semibold bg-accent text-accent-fg hover:opacity-90 transition"
            >
              <Youtube className="w-4 h-4" />
              {t("feed.yt.searchFor", { query: filters.q.trim() })}
            </button>
          )}
        </div>
      ) : (
        <VirtualFeed
          items={items}
          view={view}
          onState={onState}
          onToggleSave={onToggleSave}
          onOpenChannel={handleOpenChannel}
          onResetState={onResetState}
          onOpen={openVideo}
          hasNextPage={!!hasNextPage}
          isFetchingNextPage={isFetchingNextPage}
          fetchNextPage={fetchNextPage}
        />
      )}
      {activeVideo && (
        <PlayerModal
          video={activeVideo.video}
          startAt={activeVideo.startAt}
          onClose={() => setActiveVideo(null)}
          onState={onState}
          onOpenChannel={onOpenChannel}
        />
      )}
      {isFetchingNextPage && (
        <div className="text-center text-muted py-4">{t("feed.loadingMore")}</div>
      )}
    </div>
  );
}
